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Flow measurement

Differential Pressure Flow Calculator

Calculate flow from differential pressure using the square-root DP-to-flow relationship used with orifice plates, venturis and other differential-pressure primary elements.

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Engineering guide

How to use this calculator

  1. 1

    Enter the reference flow and reference differential pressure.

  2. 2

    Enter the measured differential pressure.

  3. 3

    Use consistent DP units for both pressure values.

  4. 4

    Calculate the estimated flow at the measured DP.

About the calculation

For many differential-pressure flow measurements, flow is proportional to the square root of differential pressure when the primary element, fluid density and operating conditions remain consistent. This lets a known reference flow and DP be used to estimate another operating point.

Use this DP flow calculator for quick transmitter checks and preliminary estimates. It is not a substitute for a full orifice, venturi or nozzle sizing calculation because discharge coefficient, density, expansibility, Reynolds number and geometry can affect actual flow.

Common engineering calculations
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Calculation method

Formula and assumptions

Q = Cd × A₂ × √(2ΔP ÷ ρ) ÷ √(1 − β⁴)

This is a simplified incompressible estimate. It does not replace a calculation to the applicable flow-measurement standard, including expansibility and tapping corrections.

Practical checks

Examples and guidance

  • The beta ratio is the orifice diameter divided by the pipe internal diameter.
  • Use a discharge coefficient appropriate to the actual plate, taps and Reynolds-number range.
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Product recommendation

These product families are the closest match to the engineering task above. Final selection depends on range, process media, temperature, pressure, connection and installation details.

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Calculator help

Questions and answers

Can this be used for gases or steam?

No. The calculator is intentionally limited to incompressible liquids. Gas and steam calculations require density and expansibility treatment at operating conditions.

Why is the discharge coefficient required?

Actual flow contracts and loses energy through the orifice. Cd corrects the ideal equation for the selected primary element and installation.

Can this replace an ISO 5167 calculation?

No. It is an engineering estimate for exploration and checks. Final sizing should follow the applicable standard and verified process data.

Application support

Share your medium, range, connection and operating conditions with our instrumentation team.

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